The application described herein relates to a semiconductor memory, and more particularly, relates to a nonvolatile memory device and an operating method of a memory controller.
A semiconductor memory device is a storage device which is fabricated using semiconductors such as, but not limited to, silicon (Si), germanium (Ge), gallium arsenide (GaAs), and indium phosphide (InP). Semiconductor memory devices are classified into volatile memory devices and nonvolatile memory devices.
The volatile memory devices may lose contents stored therein at power-off. The volatile memory devices include the following: a static RAM (SRAM), a dynamic RAM (DRAM), and a synchronous DRAM (SDRAM). The nonvolatile memory devices may retain stored contents even at power-off. The nonvolatile memory devices include the following: a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory device, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), and a ferroelectric RAM (FRAM).
The flash memory is widely used due to advantages including the following: low noise, low power, and fast operating speed. For example, the flash memory is used as a storage medium of mobile systems, such as a smart phone, a tablet PC, and so on.
The flash memory contains semiconductor elements, such as a floating gate memory cell and a charge trap flash (CTF) memory cell. In particular, the CTF memory cell traps charge in a charge storage layer to vary a threshold voltage of the CTF memory cell and thereby stores data. Charge stored in the charge storage layer moves into a channel layer with the lapse of time, so its threshold voltage varies (i.e., its threshold voltage decreases). This phenomenon is called IVS (Initial Verify Shift). Data stored in the CTF memory cell may be lost due to the IVS. There is required a program management method to solve the above-described problem.